In recent years, in order to enable long-hour use of various kinds of mobile electronic devices such as laptop personal computers and portable phones without charging, attempts have been made to use fuel cells as power sources of these portable electronic devices. The fuel cell has a feature that it is capable of generating electricity only by being supplied with a fuel and air and is capable of continuously generating electricity for long hours by being replenished with the fuel. Therefore, the fuel cell can be the to be an extremely advantageous system as a power source of portable electronic devices if it can be made compact.
A direct methanol fuel cell (DMFC) is expected to be a promising power source of portable electronic devices because it can be made compact and its fuel can be handled easily. As a method of supplying a liquid fuel in the DMFC, there have been known an active method such as a gas supply type and a liquid supply type, and a passive method such as an internal vaporization type in which a liquid fuel in a fuel storage unit is vaporized inside the cell to be supplied to a fuel electrode.
Among them, the passive method such as the internal vaporization type is especially advantageous in terms of the miniaturization of the DMFC. There has been proposed a passive-type DMFC which is structured such that, for example, a membrane electrode assembly (fuel cell unit) having a fuel electrode, an electrolyte membrane, and an air electrode is disposed on a fuel storage unit made of a resin box-shaped container (see, for example, reference 1). In the direct supply of a fuel vaporized from the fuel storage unit to the fuel cell unit, it is important to enhance controllability of an output of the fuel cell, but sufficient controllability has not necessarily been obtained in the current passive-type DMFC.
Meanwhile, it has been under consideration to connect a fuel cell unit of a DMFC and a fuel storage unit via a flow path (see references 2 to 4). Since a liquid fuel supplied from the fuel storage unit is supplied to the fuel cell unit via the flow path, it is possible to adjust a supply amount of the liquid fuel based on the shape, diameter, and the like of the flow path. However, depending on the structure for supplying the liquid fuel from the flow path, a supply state of the fuel to the fuel cell unit becomes uneven, which may possibly lower an output of the fuel cell. For example, depending on the shape of the flow path and a supply method of the fuel from the flow path, the fuel is sequentially consumed as the liquid fuel flows in the flow path, so that the concentration of the fuel at an end side of the flow path becomes low. Therefore, in the fuel cell unit, an electricity generation reaction becomes inactive in its portion close to the end of the flow path, resulting in a decrease in the output.
The patent document 3 describes that a pump is used to supply a liquid fuel from a fuel storage unit to a flow path. The patent document 3 also describes that a means for forming an electric field forming an electroosmosis flow is used instead of the pump. The patent document 4 describes that an electroosmosis flow pump is used to supply a liquid fuel or the like. A pump is effective in a fuel cell employing a fuel circulating structure, but in a fuel cell such as a passive-type DMFC in which a fuel is not circulated, the simple use of a pump only results in an increase in a consumption amount of the fuel and makes it difficult to cause a uniform electricity generation reaction in the whole fuel cell unit.    Reference 1: WO 2005/112172 A1    Reference 2: JP-A 2005-518646 (KOKAI)    Reference 3: JP-A 2006-085952 (KOKAI)    Reference 4: US 2006/0029851 A1